Pneumatic rubber tires are conventionally prepared with a rubber tread. Such tread is often composed of a blend of various rubbers.
In one aspect, truck tires, which are normally expected to be capable of carrying relatively large vehicular loads, tend to generate a greater integral temperature than comparable passenger vehicle-type tires. Accordingly, it is desired to provide truck tires which generate less heat under an operational load since higher tire running temperatures tend to prematurely age the tire rubber and, thus, shorten the effective life of the tire.
In another aspect, it is desired to provide a rubber tire tread, suitable for use on various truck vehicles, which generate less heat under operational conditions, yet also have good treadwear and wet traction (skid resistance).
It is recognized that tires have been prepared having treads based on various rubber blends of two or more rubbers, such as, for example, from two or more of styrene/butadiene copolymers (SBR), cis 1,4-polyisoprene including natural rubber, cis 1,4-polybutadiene and styrene/isoprene/butadiene terpolymers.
Tires have been taught, for example, which have a tread composed of natural rubber, a tread composed of a dual blend of SBR and cis 1,4-polybutadiene; of natural rubber and SBR (see The Vanderbilt Rubber Handbook, 13th Edition (1990) pp 603 and 604) and treads composed of tri-blends such as SBR (40-60 phr) with 30-35 percent styrene, cis 1,4-polyisoprene (20-30 phr) and cis 1,4-polybutadiene (20-30 phr).
It is to be appreciated that truck tires are often composed of natural rubber or a blend of rubbers which requires the presence of natural rubber. The natural rubber presence is usually desired to add heat durability for the tire tread.
It is recognized that various carbon blacks have been used for the reinforcement of rubber in rubber treads for truck tires which are based on natural rubber. However, for such applications, it is believed that carbon blacks characterized by having dibutylphthalate numbers of less than 130, usually less than 120, and with an ASTM series designation of N200 or above (see The Vanderbilt Rubber Handbook, Rubber Handbook, 1978 edition, pp. 414-418 for carbon black descriptions) are suitable.